This invention relates to a method of producing polyetherester monomer and cement dispersion agents (or cement dispersants). It has been known to produce polyetherester monomer as an intermediate product by an esterification reaction of polyalkyleneglycol with a closed end and unsaturated carboxylic acid and to copolymerize this polyetherester monomer with vinyl monomers which are copolymerizable therewith to obtain vinyl copolymers that can be used widely as a dispersant, an antistatic agent, an antifogging agent, an emulsifier or an adherent. In such applications, the quality of the monomer to be used in such a copolymerization reaction, and in particular the quality of polyetherester monomer, is known to significantly affect the quality of the produced vinyl copolymer serving as a dispersant, an antistatic agent, an antifogging agent, an emulsifier or an adherent. In other words, if the quality of polyetherester monomer obtained as the intermediate product is not sufficiently high, vinyl copolymers produced therefrom cannot function satisfactorily as a dispersant, an antistatic agent, an antifogging agent, an emulsifier or an adherent.
U.S. Pat. Nos. 4,962,173 and 5,362,829, for example, disclosed water-soluble vinyl copolymers having polyalkyleneglycol chain as a side chain serving as cement dispersants capable of providing a superior fluidity characteristic with a small slump loss to hydraulic cement compositions such as mortar and concrete. Such a water-soluble vinyl copolymer is usually produced by first preparing polyetherester monomer as an intermediate product by an esterification reaction of polyalkyleneglycol with a closed end and unsaturated carboxylic acid and then copolymerizing it with vinyl monomers capable of copolymerizing therewith. In this case, the quality as a cement dispersant of the water-soluble vinyl copolymer which is obtained is significantly dependent on the quality of the monomer, and in particular that of polyetherester monomer, that is used in the copolymerization reaction. In other words, if the polyetherester monomer serving as an intermediate product is of a poor quality, fluidity cannot be provided to a satisfactory manner to a hydraulic cement composition when the water-soluble vinyl copolymer obtained therefrom is used as a cement dispersant. The fluidity which has been provided has a large slump loss in such a case, and products obtained by hardening such a hydraulic cement composition have a low compressive strength.
As disclosed in Japanese Patent Publication Tokkai 11-71151, such polyetherester monomers as described above have conventionally been produced by using an organic solvent with a low boiling point such as benzene in an esterification reaction of polyalkyleneglycol with a closed end and unsaturated carboxylic acid. Use of such an organic solvent with a low boiling point is advantageous in that it is possible to obtain polyetheresters of a fairly high quality. On the other hand, the solvent which has been used for the reaction must be collected and the cost of equipment therefor adds to the total production cost of the polyetherester, or that of the vinyl copolymer to be used as the intermediate product and that of the water-soluble vinyl copolymers serving as a cement dispersant. In addition, the workers will be forced to work in an undesirable environment due to some of the properties of these substances.
It is therefore an object of this invention to provide a method of producing polyetherester monomer of a high quality without using a solvent.
It is another object of this invention to provide water-soluble vinyl copolymers capable of serving as a cement dispersant with improved properties, obtainable from such polyetherester monomer.
The present inventors discovered, as a result of work in view of the above objects, firstly that polyetherester monomer of a high quality can be obtained by an esterification reaction of polyalkyleneglycol with a closed end and unsaturated carboxylic acid under a specified condition in the presence of a specified amount of p-benzoquinone and/or phenothiazine and in the absence of any solvent, and secondly that water-soluble vinyl copolymers obtained by a radical copolymerization reaction of this polyetherester monomer with vinyl monomers which are copolymerizable therewith in an aqueous solution have improved properties as a cement dispersant.
This invention relates, on one hand, to a method of producing polyetherester monomer shown by Formula 3 given below, by causing an esterification reaction of polyalkyleneglycol with a closed end shown by Formula 1 given below and unsaturated carboxylic acid shown by Formula 2 given below by using an acid catalyst under a heated and reduced-pressure condition in the absence of solvents and in the presence of p-benzoquinone and/or phenothiazine in an amount of 0.03-0.5 weight % of polyalkyleneglycol with a closed end while distilling away generated water, where Formulas 1, 2 and 3 are respectively: 
where R1 and R2 are each H or methyl group, R3 is alkyl group with 1-22 carbon atoms, benzyl group, phenyl group or alkylphenyl group having alkyl group with 1-12 carbon atoms, and A is residual group obtained by removing all hydroxyl groups from polyalkyleneglycol of which the repetition number of oxyalkylene units (consisting either only of oxyethylene units or of both oxyethylene units and oxypropylene units) being 5-250. This invention relates, on the other hand, to cement dispersants characterized as comprising water-soluble vinyl copolymer obtained by a radical copolymerization reaction of polyetherester monomer produced by a method described above and vinyl monomers that can be copolymerized therewith.
According to this invention, explained more in detail, polyalkyleneglycol with a closed end shown by Formula 1 and unsaturated carboxylic acid shown by Formula 2 are caused to undergo an esterification reaction in the absence of a solvent to obtain polyetherester monomer shown by Formula 3. Examples of R3 in Formula 1 for polyalkyleneglycol with a closed end include (1) alkyl groups with 1-22 carbon atoms such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, hexyl group, octyl group, decyl group, dodecyl group, tetradecyl group, hexadecyl group, octadecyl group, eicosanyl group and docosanyl group; (2) benzyl group; (3) phenyl group; and (4) alkylphenyl groups having alkyl group with 1-12 carbon atoms such as methylphenyl group, ethylphenyl group, propylphenyl group, isopropylphenyl group, butylphenyl group, hexylphenyl group, octylphenyl group, nonylphenyl group and dodecylphenyl group. Among these, however, alkyl groups with 1-12 carbon atoms and benzyl group are preferable and alkyl groups with 1-3 carbon atoms are even more preferable.
As for A in Formulas 1 and 3, examples thereof include (1) residual groups obtained by removing all hydroxyl groups from polyethyleneglycol of which the oxyalkylene units are all oxyethylene units and (2) residual groups obtained by removing all hydroxyl groups from polyethylene-polypropyleneglycol of which the oxyalkylene units include both oxyethylene units and oxypropylene units, but residual groups obtained by removing all hydroxyl groups from polyethyleneglycol are preferred. If residual groups obtained by removing all hydroxyl groups from polyethylene-polypropyleneglycol are used as A, the repetition of its oxyethylene and oxypropylene units may be by random and/or block connections. The repetition number of the oxyalkylene units in the residual group representing A is 5-250, and is preferably 7-90.
Examples of polyalkyleneglycol with a closed end shown by Formula 1 include methoxy polyethyleneglycol, methoxy polyethyleneglycol-polypropyleneglycol, ethoxy polyethyleneglycol, ethoxy polyethyleneglycol-polypropyleneglycol, propoxy polyethyleneglycol, propoxy polyethyleneglycol-polypropyleneglycol, butoxy polyethyleneglycol, lauryloxy polyethyleneglycol, butoxy polyethyleneglycol-polypropyleneglycol, benzyloxy polyethyleneglycol, benzyloxy polyethyleneglycol-polypropyleneglycol, phenoxy polyethyleneglycol, phenoxy polyethyleneglycol-polypropyleneglycol, alkylphenoxy polyethyleneglycol, and alkylphenoxy polyethyleneglycol-polypropyleneglycol.
Examples of unsaturated carboxylic acid shown by Formula 2 include methacrylic acid, acrylic acid and crotonic acid. Among these, methacrylic acid is desirable.
According to this invention, polyetherester monomer shown by Formula 3 is obtained by causing polyalkyleneglycol with a closed end shown by Formula 1 and unsaturated carboxylic acid shown by Formula 2 as explained above to undergo an esterification reaction by using an acid catalyst under a heated and reduced-pressure condition in the absence of solvents and in the presence of p-benzoquinone and/or phenothiazine while distilling away generated water. The amount of p-benzoquinone and/or phenothiazine to be present in this reacting system should be 0.03-0.5 weight %, and preferably 0.1-0.25 weight %, of polyalkyleneglycol with a closed end shown by Formula 1. In particular, the presence of p-benzoquinone in an amount of 0.1-0.25 weight % of polyalkyleneglycol with a closed end shown by Formula 1 is preferable. If the amount of p-benzoquinone and/or phenothiazine present in the reacting system is less than 0.03 weight % of polyalkyleneglycol with a closed end shown by Formula 1, there is not sufficient effect of preventing polymerization. If it is greater than 0.5 weight %, on the other hand, the effect of preventing polymerization is sufficient but the radical copolymerization reaction does not proceed smoothly when the polyetherester monomer thus obtained is used as an intermediate product to produce vinyl copolymers.
The heating at the time of the aforementioned esterification reaction should preferably be to the temperature range of 105-135xc2x0 C. and the pressure in the range of 15-0.5 kPa. The heating and the lowering of the pressure should preferably be carried out either continuously or in a stepwise manner within the ranges given above.
Examples of the acid catalyst to be used in the esterification reaction include sulfuric acid, p-toluene sulfonic acid, phosphoric acid and methane sulfonic acid. They may be used either singly or as a mixture but it is preferable to use sulfuric acid singly or a mixed acid of sulfuric acid and p-toluene sulfonic acid. The amount of the acid catalyst to be used is preferably 0.2-1.5 weight % of the total of polyalkyleneglycol with a closed end shown by Formula 1 and unsaturated carboxylic acid shown by Formula 2.
The ratio between the amounts of polyalkyleneglycol with a closed end shown by Formula 1 and unsaturated carboxylic acid shown by Formula 2 to be used in the esterification reaction should preferably be 1/1.5-1/7 (in molar ratio). After the esterification reaction, the excess portion of unsaturated carboxylic acid is distilled away.
The method of producing polyetherester monomer according to this invention is explained next further in detail. When methoxy polyethyleneglycol methacrylate, for example, is produced as the polyetherester monomer of this invention, methoxy polyethyleneglycol and an excess amount of methacrylic acid are placed inside a reactor and a specified amount of p-benzoquinone and/or phenothiazine serving as a polymerization inhibitor, appropriate for the amount of the methoxy polyethyleneglycol and a specified amount of concentrated sulfuric acid serving as an acid catalyst are added into the reactor. Next, the temperature of the reacting system is gradually raised and its pressure is gradually lowered until a specified temperature-pressure condition is reached. An esterification reaction is carried out under this temperature-pressure condition while water which is generated is removed by azeotropic distillation of water and methacrylic acid. After the esterification reaction, the excess portion of methacrylic acid is removed to obtain methoxy polyethyleneglycol methacrylate. The polyetherester monomer thus obtained contains the aforementioned polymerization inhibitor and acid catalyst but it may be directly used as an intermediate product for the production of vinyl copolymers without refining to remove them.
Next, cement dispersants according to this invention will be described. The cement dispersants of this invention are characterized as comprising water-soluble vinyl copolymers obtained through the following two steps, the first step being that of obtaining polyetherester monomer shown by Formula 3 as described above, that is, by causing an esterification reaction of polyalkyleneglycol with a closed end shown by Formula 1 and unsaturated carboxylic acid shown by Formula 2 by using an acid catalyst under a heated and reduced-pressure condition in the absence of solvents and in the presence of p-benzoquinone and/or phenothiazine in an amount of 0.03-0.5 weight % of the polyalkyleneglycol with a closed end while distilling away generated water, and the second step being that of obtaining water-soluble vinyl copolymers by a radical copolymerization reaction of the polyetherester monomer obtained in the first step with vinyl monomers which are copolymerizable with it inside an aqueous solution.
Any of known kinds of vinyl monomers can be used in the second step as long as they are copolymerizable with polyetherester monomer. Examples of such vinyl monomer include ethylenic unsaturated monocarboxylic acids and/or their salts, ethylenic unsaturated dicarboxylic acids and/or their salts, ethylenic unsaturated monocarboxylic acid esters, unsaturated carboxylic acid esters with hydroxyl group, aromatic vinyl monomers, vinyl monomers with amino group, vinyl monomers with amide group, vinyl monomers with aldehyde group, vinyl monomers with nitrile group, vinyl esters, alkene compounds, dien compounds and vinyl monomers having sulfonic acid group. Among these, ethylenic unsaturated monocarboxylic acids and/or their salts and vinyl monomers with sulfonic acid group are desirable. Particularly preferable are (1) (meth)acrylic acids and/or their salts such as (meth)acrylic acid, alkali metal salts of (meth)acrylic acid, alkali earth metal salts of (meth)acrylic acid and organic amine salts of (meth)acrylic acid, and (2) methallyl sulfonic acid salts to be used with such (meth)acrylic acids and/or their salts such as alkali metal salts of methallyl sulfonic acid, alkali earth metal salts of methallyl sulfonic acid and organic amine salts of methallyl sulfonic acid.
The invention does not impose any particular limitation on the copolymerization ratios of polyetherester monomer and vinyl monomers which are copolymerizable therewith but in the case of radical copolymerization of polyetherester monomer and (meth)acrylic acid and/or its salt, it is preferable to copolymerize 5-50 molar % of polyetherester monomer with 50-95 molar % of (meth)acrylic acid and/or its salt (such that the total will be 100 molar %), while in the case of radical copolymerization of polyetherester monomer, (meth)acrylic acid and/or its salt and methallyl sulfonic acid salt, it is preferable to copolymerize 5-45 molar % of polyetherester monomer, 50-90 molar % of (meth)acrylic acid and/or its salt and 0.3-15 molar % of methallyl sulfonic acid (such that the total will be 100 molar %).
The radical copolymerization reaction itself can be carried out in a known manner such as described, for example, in Japanese Patent Publication Tokkai 8-290948. Water-soluble vinyl copolymer can be obtained, for example, by preparing an aqueous solution containing polyetherester monomer obtained in the first step, vinyl monomers which are copolymerizable therewith and a chain transfer agent and causing a radical copolymerization reaction for 4-8 hours at reaction temperature of 50-90xc2x0 C. in a nitrogen environment by adding a radical initiator. Examples of chain transfer agent which may be used in this process include 2-mercaptoethanol, mercaptopropionic acid and mercaptoacetic acid. Examples of radical initiator include persulfates such as sodium persulfate, potassium persulfate and ammoniumn persulfate and water-soluble radical initiators such as 2,2xe2x80x2-azobis(2-amidinopropane)dihydrochloride.
The average numerical molecular weight (hereinafter Pullulan converted by GPC method) of the water-soluble vinyl copolymers thus obtained by radical copolymerization is preferably 3500-70000 and more preferably 5000-40000.
Cement dispersants embodying this invention which comprises the water-soluble vinyl copolymers may be used for many kinds of hydraulic cement compositions using not only cement but also a mixing material in a fine powder form as a binder, or mortar and concrete as typical examples. Examples of cement include different kinds of portland cement such as normal portland cement, high early portland cement and moderate heat portland cement, as well as many different kinds of blended cement such as portland blast-furnace slag cement, fly ash cement and silica pozzolan cement. Examples of mixing material in a fine powder form include lime stone powder, calcium carbonate, silica fume, blast-furnace slag powder and fly ash.
The rate at which the cement dispersants of this invention should be used is normally 0.01-2.5 weight parts and preferably 0.05-1.5 weight parts % (by solid component) for 100 weight parts of binder consisting of cement or cement and mixing powder material.
The method of producing polyetherester monomer embodying this invention is characterized in that no solvent is used in the esterification reaction of polyalkyleneglycol with a closed end shown by Formula 1 and unsaturated carboxylic acid shown by Formula 2. As an important result of this, there is no need to collect any solvent after the esterification reaction is completed. Moreover, the method of this invention is capable of producing polyetherester monomer of a high quality shown by Formula 3. As will be described in detail below, polyetherester monomer with high esterification reaction rate can be obtained without abnormal increase in viscosity or generation of gel at the time of the esterification reaction. Water-soluble vinyl copolymers using high-quality polyetherester monomer produced by a method of this invention as an intermediate product exhibit desirable characteristics as cement dispersant. They can provide fluidity to hydraulic cement compositions with only a small slump loss and hardened products obtained from such hydraulic cement compositions have improved compressive strength.